Telephone answering devices are commonly controlled by microprocessors. The microprocessor typically controls a multiplicity of peripheral components of the telephone answering device which may include, for instance, an LCD or LED display, a recording and playback device, indicator lights, a DTMF (Dual Tone Multi-Frequency) receiver and an audio controller. Input and/or output ports of the microprocessor are hardwired to the peripheral component that it controls.
Typically, a plurality of ports are dedicated to each peripheral component for controlling various functions of that component. For instance, U.S. Pat. No. 4,400,586 discloses a typical prior art telephone answering device having a microprocessor which is connected to the various peripheral components of the device through a plurality of ports. A port on the microprocessor and an associated lead are provided for each data or instruction bit needed to control and/or provide data to each peripheral component.
This type of design has several drawbacks. First, telephone answering device manufacturers commonly improve and update their products from time to time to add features and, consequently, components to earlier models. A telephone answering device designed with a communication/control configuration as described above requires substantial hardware redesign if it is desired to add additional peripheral components and functions. In order to add additional components and functions, pins must be added to the microprocessor and conductor leads must be added between those pins and the new components. Accordingly, minor updating or modifying of telephone answering devices required sometimes significant hardware redesign. Accordingly, it is an object of the present invention to provide an improved peripheral component control structure for a telephone answering device.
It is a further object of the present invention to provide a telephone answering device with a standardized internal bus.
It is another object of the present invention to provide a telephone answering device which can be modified easily and inexpensively to add or change peripheral components.
It is yet another object of the present invention to provide a telephone answering device which can be modified to add additional peripheral components and functions without adding significant additional data lines or ports to the microprocessor controller.